Assemblies of lithium-ion battery cells are finding increasing applications in providing electric power in automotive vehicles and in computers, lamps, and in many other non-automotive, consumer and aerospace applications.
Each lithium-ion cell of the battery is capable of providing an electrical potential of about three to four volts and a direct electrical current, based on the composition and mass of the electrode materials in the cell. The cell is capable of being discharged and charged over many cycles. A battery is assembled for an application by combining a suitable number of individual cells in a combination of parallel and series electrical connections to satisfy voltage and current requirements, for example, for a specified electric motor used in driving an automotive vehicle. In a lithium-ion battery application for an electrically powered vehicle, the assembled battery may, for example, comprise up to three hundred individually packaged cells that are electrically interconnected to provide forty to four hundred volts and sufficient electrical power to an electrical traction motor to drive a vehicle. The direct current produced by the battery may be converted into an alternating current for more efficient motor operation.
In these automotive applications, each lithium-ion cell typically comprises a negative electrode layer (anode, during cell discharge), a positive electrode layer (cathode, during cell discharge), a thin porous separator layer interposed in face-to-face contact between parallel, facing electrode layers, and a liquid, lithium ion-containing, electrolyte solution filling the pores of the separator and contacting the facing surfaces of the electrode layers for transport of lithium ions between the electrodes during repeated cell discharging and charging cycles. Each electrode is prepared to contain a layer of a porous electrode material, typically deposited as a polymer resin-coated mixture of particles on a thin layer of a compatible metallic current collector.
For example, the negative electrode material has been formed by spreading a thin layer of graphite particles or lithium-accepting alloy or oxide and a suitable polymeric binder onto one or both sides of a thin foil of copper (or aluminum, for high voltage negative electrodes) which serves as the current collector for the negative electrode. The positive electrode often comprises a thin layer of resin-bonded, porous, particulate lithium-metal-oxide composition spread on and bonded to a thin foil of aluminum, which serves as the current collector for the positive electrode. The positive and negative electrodes may be formed on conductive metal current collector sheets of a suitable area and shape, and cut (if necessary), folded, rolled, or otherwise shaped for assembly into lithium-ion cell containers with suitable porous separators and a liquid electrolyte.
There remains a need to improve the performance of certain lithium-ion cells to reduce capacity-fading of the cells due to unwanted consumption of lithium ions in the cells.